1. Field of the Invention
The present invention relates to a cutting method for substrates in which the cutting of the substrates is performed and the forming of grooves on substrates (for example, semiconductor wafers) by using a cutting blade.
2. Description of the Related Arts
Semiconductor devices (for example, semiconductor chips) are produced by the following processes. That is, a wafer (for example, a semiconductor wafer) which is composed of a semiconductor substrate material is prepared. Grid-like predetermined division lines are formed on a surface of the wafer, so that plural rectangular device regions are defined by the predetermined division lines on the surface of the wafer. Next, electronic circuits (for example, Integrated Circuits (=ICs) and Large Scale Integrations (=LSIs)) are formed on the device regions. Next, a rear surface of the wafer is ground, so that the wafer is thinned to have a desired thickness. Next, the wafer is divided along the predetermined division lines. As a result, the semiconductor devices (for example, semiconductor chips) are produced. In the above processes, in order to prevent the occurrence of damage (for example, cracking and breakage) in the wafer during handling of the wafer, a circumferential edge of the wafer may be chamfered before the thinning of the wafer.
When a wafer having a chamfered circumferential edge is thinned, the circumferential edge in a cross section is outwardly sharper and thinner so as to have a knife edge shape. Since the same damage may easily occur again in the above condition of the circumferential edge, the circumferential edge is subjected to cutting before thinning of the wafer so as not to have a knife edge shape, so that the circumferential edge has a surface which extends along a thickness direction of the wafer (which extends perpendicularly to a surface of the wafer) as disclosed in Japanese Unexamined Patent Application Publication No. 2000-173961. If damage (for example, cracking and breakage) occurs at the circumferential edge, the circumferential edge may be the origin of damage which extends to device regions having electronic circuits formed thereon, and the wafer itself may break and become unusable. Therefore, the above cutting of the circumferential edge is advantageous.
The cutting for preventing the generation of a knife edge shape is performed by forming either a ring-shaped step or a circular groove on a circumferential edge proximate to a surface of a chamfered wafer before thinning. The step and the groove have circular shapes which have diameters corresponding to a diameter of the wafer finally obtained and which have depths corresponding to a desired thickness of the wafer obtained after thinning. When a rear surface of the wafer is thinned by grinding, the circumferential edge does not have a knife edge shape and has a surface extending along a thickness direction as disclosed in Japanese Unexamined Patent Application Publication No. 2000-173961 (in particular, FIGS. 2 to 4).
The above cutting of the circumferential edge uses the following method. That is, a wafer is held horizontally so that a surface thereof faces upward. A cutting blade, which is rotated at a high speed and is positioned above the wafer, is moved downward and cuts a layer of the wafer, which has a predetermined depth from the surface thereof, at a cutting start point on the wafer. From this condition, the cutting blade is rotated relatively to the wafer, thereby cutting the wafer in a horizontal direction.
In addition, in the field of semiconductor devices, there is a case in which a wafer having a small diameter is obtained from a wafer having a relatively large diameter by cutting. In this case, a cutting blade is moved downward and then cuts a layer, which has a predetermined depth from a surface of the wafer, in a horizontal direction as disclosed in Japanese Unexamined Patent Application Publication No. H11-54461.
The cutting blade disclosed in Japanese Unexamined Patent Application Publications described above is coaxially provided at an end of a spindle having a rotation shaft. In general, the spindle is movably supported by a frame or the like in a horizontal direction, which extends along an axis of the spindle, and in a vertical direction while the axis thereof is maintained in a horizontal direction. In general, in the moving of the cutting blade, the downward speed of the cutting blade is relatively slower than the horizontal speed thereof. In addition, when the cutting blade cuts the wafer, there is a limit to setting the downward speed of the cutting blade to be faster in order to prevent a warp of the cutting blade due to a large load applied thereon. Due thereto, the downward speed of the cutting blade is small, the moving of the cutting blade to the cutting start point on the wafer is time-consuming for manufactures, and production efficiency is not good.